Question: The arithmetic sequence $(a_i)$ is defined by the formula: $a_i = 9 + 5(i - 1)$ What is $a_{18}$, the eighteenth term in the sequence?
Answer: From the given formula, we can see that the first term of the sequence is $9$ and the common difference is $5$ To find $a_{18}$ , we can simply substitute $i = 18$ into the given formula. Therefore, the eighteenth term is equal to $a_{18} = 9 + 5 (18 - 1) = 94$.